Uploading photos to photo printing website

The thing is, drag and drop isn't actually supported in Photos. What happens when you use that process seems to depend on which version you're in, or maybe where you drop it or, well, we don't know because it's not supported-- it's not documented.. Sometimes you get the preview; sometimes the thumbnail; sometimes the un-edited version; sometimes the original--sometimes you get nothing at all. I imagine different people might expect it to do different things, since there are so many different versions of the pictures. I will drag and drop into a text or maybe an email or other places where it doesn't matter much, but I look to see if I got what I wanted. If it's worked for you, you were lucky.

You can use the upload routine from the browser but, for me, to get what I want I use File>Export>Export nn Photos and put the pictures in a folder on the desktop. I can control the picture's size and quality and strip or include personal metadata. I may then drag them from the folder to the web page, and delete the folder later.